I doubt whether you're the worlds worst photographer. We can't see your photographs, so we can only speculate on why they are being rejected. However, my tuppence worth is as follows:
My impression is that rejections fall broadly into three categories:
1. Bad original picture - too grainy (wrong film), out of focus, blurred, incorrectly exposed, etc.
2. Bad composition - bits chopped off, subject too small, things in the way, sloping horizons, etc.
3. Bad scan - contrast or exposure wrong, too grainy, etc.
You need to consider why your pictures are being rejected and sort out that particular problem.
If your rejections fall into group (1) above, the pictures are probably mostly unrecoverable and you need to go shoot some more pictures. Take note of the comments about sunny days and static shots to start with. But I doubt (1) is the problem as I doubt you are the world's worst photographer!
If its (2) that is the problem, there may be something you can do post-scanning to correct the problems - you can't bring back bits that were chopped off when the photo was taken, but you can correct horizons and you may even be able to crop out distracting stuff in the foreground etc. But if it is this that's the problem, next time you take some pictures, you need to pay more attention to the composition - don't rush your pictures and make sure everythings OK before you press the button.
However, seems to me that most people, when they have a problem, have a problem with (3). If this is the case, you need to practice and experiment with your scanning and post-scanning technique. Read the FAQs to make sure you're not falling foul of the image size, resolution or other rules that apply to uploads. Read the threads on scaning technique on this forum and try some of them. Have a look at other scanning sites like scantips. Look critically at your end result through a browser so you see it as it will be seen on airliners.net. Look carefully at the large versions of images on airliners.net to see if the sharpness, contrast, grain etc on your pictures are equivalent to the pictures that are already on airliners.net. If they're not, adjust your scanning technique and try again.
Whatever you do, give yourself a fighting chance. Start off with what you regard as your better / best pictures, or pictures of something interesting that isn't already on airliners.net - don't choose the stuff you shot most recently or stuff that's close to hand unless these are your best.
Finally, whatever the reason for your rejections, be honest with yourself - if what you see through a browser after you have scanned, cropped, retouched and saved as a jpeg is not as good as the majority of stuff already on this web-site, I'd honestly suggest that you don't upload the end result but instead start again with the scanning, etc. If you upload stuff that you know in your heart of hearts is not as good as what's already on this site, you know what will happen - don't subject yourself to that until you are as close as you can get to being 100% happy with what you are uploading. And if at the end of the day you can't make it work, ask some specific questions about the problem as you see it - there's people here who will try to help.